Winter-to-summer evolution of pCO2 in surface water and air–sea CO2 flux in the seasonal ice zone of the Southern Ocean

[摘要] Partial pressure of CO₂ (pCO₂) in surface waterand vertical profiles of the carbonate system parameters were measuredduring austral summer in the Indian sector of the Southern Ocean(64–67° S, 32–58° E) in January 2006 to understand theCO₂ dynamics of seawater in the seasonal ice zone. Surface-waterpCO₂ ranged from 275 to 400 μatm, and longitudinal variationsreflected the dominant influence of water temperature and dilution bysea ice meltwater between 32 and 40° E and biologicalproductivity between 40 and 58° E. Using carbonatesystem data from the temperature minimum layer(−1.9 °C < T < −1.5 °C, 34.2 < S < 34.5), we examinedthe winter-to-summer evolution of surface-water pCO₂ and the factorsaffecting it. Our results indicate that pCO₂ increased by as much as 32 μatm,resulting mainly from the increase in water temperature. At the same time as changes in sea ice concentration and surface-water pCO₂,the air–sea CO₂ flux, which consists of the exchange of CO₂ between sea iceand atmosphere, changed from −1.1 to +0.9 mmol C m⁻² day⁻¹between winter and summer. These results suggest that, for the atmosphere,the seasonal ice zone acts as a CO₂ sink in winter and a temporaryCO₂ source in summer immediately after the retreat of sea ice.Subsequent biological productivity likely decreases surface-water pCO₂and the air–sea CO₂ flux becomes negative, such that in summer the studyarea is again a CO₂ sink with respect to the atmosphere.

[学科分类] 地球化学与岩石